About 74,000 years ago, the Toba volcano on the Indonesian island of Sumatra erupted with catastrophic force. Estimated to be 5,000 times larger than the 1980 eruption of Mount St. Helens, it is believed to be the largest volcanic event on Earth in the last 2 million years.

Toba spewed enough lava to build two Mount Everests, it produced huge clouds of ash that blocked sunlight for years, and it the left behind a crater 31 miles (50 kilometers) across. The volcano even sent enough sulphuric acid into the atmosphere to create acid rain downpours in the Earth's polar regions, which researchers have found evidence of in deep ice cores.

"We have now traced this acid rain in the ice caps on Greenland and Antarctica," glaciologist Anders Svensson, of the Niels Bohr Institute at the University of Copenhagen, said in a statement.

"We have long had an idea of at what depth the Toba eruption could be found in the Greenland ice cap, but we found no ash, so we could not be sure," Svensson added. "But now we have found the same series of acid layers from Toba in the Greenland ice sheet and in the ice cap in Antarctica. We have counted the annual layers between acid peaks in ice cores from the two ice caps and it fits together."

Scientists have long debated just how extensive and enduring those effects were. One study, for example suggested the Toba blast spawned a thousand-year ice age that only some 10,000 individuals survived. Another has found evidence of humans thriving in relatively nearby India shortly after the eruption.

The new study -- based on acid rain-tainted ice cores from Antarctica and Greenland -- suggests Toba's fallout wasn't quite as catastrophic as might be expected.

The Antarctic ice core, for example, even bears traces of a warming event just after the Toba eruption -- contrary to a strong cooling signal seen in the Greenland cores.

"That means there's no long-term global cooling caused by the eruption," study co-author Anders Svensson said. If there had been, you'd expect to see evidence of a chill at both Poles.

In fact, the post-Toba Antarctic cooling spike looks well, relatively ordinary. "There may have been shorter [global] cooling of a duration of maybe 10 or 20 years, like we see for more recent" -- and much less powerful -- "volcanoes," said Svensson, of the Niels Bohr Institute's Centre for Ice and Climate in Copenhagen.

Now, a new study published in the journal Climate of the Past based on acid rain-tainted ice cores from Antarctica and Greenland, suggests Toba's wasn't effect quite as catastrophic as might be expected. The Antarctic ice core shows traces of a warming event soon after the Toba eruption in contrast to vivid cooling signs found in the Greenland ice cores.

"That means there's no long-term global cooling caused by the eruption," study co-author Anders Svensson of the Niels Bohr Institute's Centre for Ice and Climate in Copenhagen said. If there had been, you'd expect to see evidence of a chill at both Poles. There may have been shorter cooling of a duration of maybe 10 or 20 years, like we see for more recent and much less powerful volcanoes."

The current Ice Age currently breaks down into two broad climate types ~ (1) lots more ice for 100,000 years. Toba occurred when there was lots more ice than presently, and (2) less ice for a period of 10,000 years or more. We are in an interglacial that's been around for 14,000 years.

There are shorter warm spells in the midst of the icy periods ~ Toba might well have occurred during such a period, or could have influenced it in some way.

I’m no scientist, so feel free to chime in here, but... wouldn’t this have caused the sort of “nuclear winter” they’re always talking about with reference to a nuclear war - the clouds eliminating all sunlight until all the plants died and so on?

That’s a good point — the fact that it didn’t have that kind of effect goes to show just how pipsqueakish ALL volcanic eruptions are compared with impacts by large pieces of space debris. It’s remarkable how mealy-mouthed this is carried out — oh, the Chicxulub impact didn’t do anything *because dinosaurs were already in the _process_ of going extinct* (emphasis on stuff that makes no sense, more emphasis on stuff that really makes no sense), but this big eruption field called the Deccan Traps caused the mass extinction. Meanwhile this 70K year old supereruption caused the (entirely imaginary) genetic bottleneck in the human species, and only them, and we know its exact extent, era, and duration. Ridiculous.

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